All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
Michael O'Pray: The prediction for ArqB for you is much better than for Mux A and C. If you're only having trouble with channels on ArqB (such as the one you've mentioned) I'd check for damp in cables and connector boxes. Higher frequencies have much more attenuation in cables, particularly where water has seeped in, than low ones - and ArqB is all the way at the top of the frequency range, while the PSB multiplexes are all the way at the bottom. The other two commercial multiplexes A and C are in the middle.
It's not particularly easy to tell what sort of cable you have just by looking at it, but the cheap 'low-loss' coax often has a brown sheath, whereas 'satellite-grade' coax cable should have something like 'CT100', 'HD100' or 'WF100' printed on it at regular intervals. 'Low-loss' might have been low loss when introduced but compared to satellite grade cable, it's pretty poor. It also picks up more interference, particularly from electrical equipment, so a re-cabling could be worthwhile.
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Michael O'Pray: Actually, looking back on your past comments, it's possible that your box isn't picking up the transmissions from Sandy Heath, but instead using the transmissions from a more distant transmitter.
Check that the box is not on the list of 2K-only equipment at TVs and boxes that do not support the 8k-mode | ukfree.tv - independent free digital TV advice .
If you can, find out which UHF channels are being used for each multiplex. BBC One, Two, Three and Four should be on C27. ITV1, C4 and C5 should be on C24. ITV3 should be on C43. Pick TV should be on C40. Film4 and ITV4 should be on C67. If not, you will have to delete the channels that have been stored incorrectly, and try manually tuning the correct frequencies.
Please see Digital Region Overlap for some more ideas of how to handle this situation.
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Stuart: The low-power digital transmissions had to be squeezed in, however it could be done, but in a way that minimized interference to anyone else's analogue TV transmissions. Digital was considered an add-on service initially. The south coast was particularly difficult due to international co-ordination. It meant restricted radiation patterns, odd frequency selections, and limited power levels. Some transmitters had to have more than one set of aerials pointing in different directions, using different frequencies, and Dover is one of those.
The switch-over is more a switch-off - a switch off of the old analogue signals so that high-power digital signals can replace them. Even then, they are not designed to cover the whole country or even the whole population - the estimate for acceptable analogue reception was 98.5%. The public service broadcasters have to match that level for digital service, the commercial multiplex operators don't.
The predictor currently shows no prediction for Mux 1, 2 and A. After switchover it shows a relatively low probability of getting reliable results, indicating variable reception.
I'd look into Freesat.
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There's also a retune at Fenton tomorrow: Mux 2 moves from C30 to C33 so The Wrekin, Bromsgrove and Lark Stoke can use C30 for the HD mux.
http://www.digitaluk.co.u….pdf
There are a number of late-breaking channel changes at relay sites, to release C61 and C62:
Clun HD C50
Eardiston D3&4 C49
Hazler Hill HD C39
Ludlow HD C39
St Briavels HD C40
Source: Postcode Checker - Trade View
Halesowen D3&4 will start on C61 and move later. I'm speculating this is because Haden Hill, which has moved to the Sutton Coldfield group, still uses C49 for ITV1 until September. The radiation patterns of the two transmitters (which are in your FoI data) seem to cover the same area.
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Mark G: It's not possible to change radiation patterns independently on an aerial. If the radiation pattern is significantly different for different channels, it's because a different aerial or set of aerials is used, or lower power levels feeding one element relative to the others. That's not going to be at all common after switchover. It might be slightly different on different channels using the same aerials and same power levels if they've taken account of how the aerial's radiation pattern changes with frequency, but that's a fundamental characteristic of the aerial's design, not something that can be tuned.
All digital transmissions from Hannington come from the panels just below the top of the mast. They're mounted on the north-west corner and are three sets of panels, pointing due west, slightly west of north, and slightly west of due south. The panels' radiation patterns are quite wide but not much beyond 90° - and the mast itself is in the way.
The changes so far for switchover have entailed replacing the top aerial used currently for analogue, and for digital after switchover, possibly changing how much analogue signal you're receiving. High signal levels can overload amplifiers and the gain control components in the tuner, which cause a problem called intermodulation or cross-modulation - parts of a signal on one channel getting copied into nearby channels. (It doesn't damage the amp, but it distorts the signals.) These intermodulation products cause extra noise. If you have an amp or booster, try removing it - reception is going to be difficult because of Guildford analogue anyway, and the amp will amplify Guildford analogue as much as it amplifies Hannington digital.
The reception change events are due to other distant transmitters switching over and either beginning to use those frequencies for the first time, releasing them, or using them for digital rather than analogue.
The change to channel 40 (Mux A) in September is likely to be Sutton Coldfield's switchover - currently it carries BBC Two analogue on C40 and on 21 September, it becomes the high-power HD multiplex. Despite the maximum power being only one-fifth the maximum power of analogue, digital signals do more harm to one another and that's reflected in Gary's prediction - a drop of 2% in probability.
You're further to the south-east, so your reception is affected more by fringe reception of Sandy Heath. Belmont's switchover on 17 August frees up C48 so ArqB at Sandy Heath can then move to that frequency on 14 September. Sandy Heath has to wait until Hemel Hempstead Mux 1 gets out of the way (also on 14 September), which presumably can't happen until after Sutton Coldfield/Emley Moor DSO 1.
This is all in order to improve ArqB on C48, which has no direct impact on Hannington. On the same day, Sandy Heath Mux C moves from C40 to C67 (where ArqB had just come from). This is for the reciprocal impact on BBC B at Sutton Coldfield.
The improvement on Mux 1 (C50) in September is more straightforward: Sutton Coldfield stops using it (currently C4 analogue). It then deteriorates again in November when Tacolneston starts using it for ArqB. I'm not sure whether it starts at lower power and increases to full power in 2012, or whether that change is due to the DTT clearance programme, which moves transmitters from C62 to C50 in order to release C62 for mobile phones.
You're probably thinking that these transmitters are a long way off, and they are - over the horizon, mostly. Signals still bounce off the atmosphere, particularly at night, and when the weather conditions are right. The DUK predictor tries to take account of all this. Besides, just because a signal is not strong enough to watch doesn't mean it isn't strong enough to interfere.
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Michael O'Pray: The Dallington Park transmitter was there to provide a four-channel service to a number of fairly small areas in Sandy Heath's coverage area: the ones in the semi-circle to the east of the transmitter in this coverage map:
mb21 - The Transmission Gallery
As Sandy Heath digital transmissions are now effectively louder than the analogue ones, these holes may no longer exist. Nearly all relays are being converted anyway, in case people are still watching them. A very few are closing and some new ones are being constructed.
There were considered to be 51 main transmitters in the country before onDigital started (some people have different counts, depending on whether you counted Torosay, for example). All of them got digital with limited coverage areas from 1997, and a further 30 sites covering areas of population considered important but not covered by the main transmitters, for example Sheffield, where Emley Moor barely touches the city, and Fenton covering Stoke-on-Trent.
There are around a further 1,000 relay transmitters in the country that didn't carry digital before switchover. The regulator, Ofcom, have decided that they can force the public service broadcasters to pay the cost of serving all these relays, but have decided not to use their powers to force the commercial multiplex operators to do so. The COMs were asked if they wanted to, and they said no - not cost-effective. The transmitter owners - before merging into one company - quoted £14m per year more for serving all transmitters compared to just the 81, nearly 2.4x as much. Satellite transmission is much cheaper.
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M
Sutton Coldfield (Birmingham, England) Full Freeview transmitteTuesday 19 April 2011 8:13PM
Reading
Brian: You can get everything *except* Mux D? The prediction is exactly the opposite. Try it without the signal booster, or if you can vary the gain, turn it down to the minimum and just increase it enough to get all the channels without break-up.
The Winter Hill transmitter is beyond Sutton Coldfield in the same direction, and it uses C55 for the ArqB multiplex. It is currently running at relatively low power, and the terrain normally blocks the signal, but in the right weather conditions it can cause enough interference to stop Mux D working.
This will no longer be a problem after switchover as Sutton Coldfield and Winter Hill will have no frequencies in common. (The Winter Hill power restriction is removed on 21 September, which is DSO Stage 2 at Sutton Coldfield.)
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M
Sutton Coldfield (Birmingham, England) Full Freeview transmitteTuesday 19 April 2011 8:20PM
Reading
Tim: 70% on a Humax 9200T is too much signal. You should reduce it to below 50%. If you have an amplifier, remove it or turn it down.
I believe the box is calibrated for a range of 35 to 95 dBuV (this is the range shown in the manual). 95 dBuV is fine in a test lab with no other signals, but the combination of all the other signals transmitted by this transmitter, and fringe reception of others, means that the recommendation before switchover is a maximum of 60-65 dBuV. 65 dBuV is half-way between 35 and 95 - 50%.
Too much signal causes a problem called intermodulation, where the distorted signal bleeds into other channels, particularly adjacent ones. Multiplexes 1, 2, A and B are adjacent to much louder analogue channels; multiplex C is next to mux B.
(I own a 9200T.)
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M
Waltham - retune required Wednesday 13 April 2011 | SwitchoversTuesday 19 April 2011 11:03PM
Reading
Things may improve slightly after tonight, when Bromsgrove stops transmitting BBC One analogue at 2.8 kW on C31 (although it does so on vertical polarization rather than horizontal). The Wrekin and Lark Stoke will continue to use C31 until after Waltham switches, The Wrekin at its current power level of 2 kW (horizontal, same as Waltham) and Lark Stoke doubling from 25W to 50W (vertical).
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Sunday 17 April 2011 9:32PM
Colin McLeod: I believe you may have too much signal. If you have any amplifiers or boosters, try removing them. If not, try adding an attenuator.
A calculation suggests that before switchover you could be getting around 73 dBuV on Mux 1, with a fairly small aerial. The accepted range was 45-60 dBuV (some give 65 dBuV as the upper limit). Analogue signal level would have been 93 dBuV on Channel 4 - accepted range was 60-80 dBuV.
Field Strength Calculator
Post-DSO signal level on BBC B is 85.5 dBuV with the same assumptions. I haven't seen a suggested upper limit for post-DSO transmissions, I would suggest somewhere around 70 dBuV as there will be six high-power DTT muxes rather than four/five analogue channels.
Brian's point was that you don't have to pay Murdoch for satellite TV. You can have free-to-air satellite TV, no subscription, ever, by just buying a Freesat box and having a dish installed. (RG47SH)